Volkswagen AG’s top U.S. executive is stepping down nearly six months after the German automaker admitted to installing software to allow vehicles to pass emissions regulations in the United States.  Regulators say Volkswagen vehicles were emitting up to 40 times more pollution than U.S. standards allow.

The Environmental Protection Agency (EPA) found that many VW cars being sold in the US had a “defeat device” – or software – in diesel engines that could detect when they were being tested, changing the performance accordingly to improve results.  The EPA’s findings cover 482,000 cars in the US only, including the VW-manufactured Audi A3, and the VW models Jetta, Beetle, Golf and Passat. But VW has admitted that about 11 million cars worldwide, including eight million in Europe, are fitted with the so-called “defeat device”.

Michael Horn has been president and chief executive officer of Volkswagen Group of America since 2014.  The German automaker said on an interim basis, Hinrich J. Woebcken, a former BMW executive who ran global purchasing among other jobs, is filling Horn’s job.  This comes about six months after the resignation of the global head of Volkswagen, Martin Winterkorn, as well as others who held senior management positions with VW.

Volkswagen faces an ongoing Justice Department criminal investigation. The Justice Department sued VW in January seeking up to $46 billion for violating environmental regulations and sent VW a civil subpoena under a bank fraud law.

During the initial response to the scandal, Horn was VW’s public face in the United States, apologizing days after the scandal became public and testifying before Congress.  “Let’s be clear about this: our company was dishonest – with the EPA and the California Air Resources Board – and with all of you. And in my German words: We totally screwed up. We must fix those cars,” Horn said.

In October, Horn told a U.S. House of Representatives panel that VW’s supervisory board and top leadership did not intentionally order the cheating, but said it was the work of a few individuals.  Horn told Congress he had no knowledge of the cheating.

Nine high-level VW managers were put on leave late last year, sources told Automotive News Europe, after the automaker’s diesel emissions cheating became public.

Alan Brown, general manager of Hendrick Volkswagen in Frisco, Texas who is president of the National Volkswagen Dealer Advisory Council, praised Horn’s tenure at VW and said he had talked to Horn about his departure. Brown told Reuters Horn had been offered other jobs at Volkswagen outside the United States, but declined to take them.